If it using Windows XP -
Goto Control Panel
Click on Display (or Appearance and themes)
Click Settings
(If the additional monitor is plugged into the laptop, then you should have a picture of 2monitors in the properties Window that opens)
One is the primary - the other is the secondary monitor.
Click once on the one you want as the primary (the one you want to to use)
To identify which is Monitor 1 or Monitor 2 click on the 'Identify' button.
Hope this help.
